Portable ground plane mat with cavity backed antennas placed thereon



was

Feb. 11, 1964 H. BRUECKMANN PORTABLE GROUND PLANE MAT WITH CAVITY BACKEDANTENNAS PLACED THEREON Filed March 1, 1961 [II/Ill I/I/I/I/I/I/I/I/I II JNVENTOR,

HELMUT BRUECKMANN ATTORNEY.

United States Patent 3,121,230 PORTABLE GROUND PLANE MAT WITH CAVITYBACKED ANTENNAS PLACED TIIEREON Helmut Brueckmann, Little Silver, NJ.,assignor to the United States of America as represented by the Secretaryof the Army Filed Mar. 1, 1961, Ser. No. 92,720 7 Claims. (Cl. 343-770)(Granted under Title 35, U.S. Code (1952), sec. 266) The inventiondescribed herein may be manufactured and used by or for the Governmentfor governmental purposes without the payment of any royalty thereon.

This invention relates to antennas and, more particularly, to aportable, low-profile antenna which is relatively immune to groundeffects.

The radiation characteristics of an antenna are affected by theelectrical properties of the ground beneath it. These ground effects canbe taken into account as long as the electrical properties of the groundare known thereby making possible adjustments of the antennacharacteristics to achieve the desired radiation pattern for an antennaat a fixcd location. However, in the case of portable antennas prior tothis invention ground effects constituted a serious problem for whichthere was no simple solution, especially for low level or low-profileantennas.

In the case of radio beacon antennas for air navigation and forcommunication and telemetering from ground to air in systems such asmissile guidance and satellite communication, the variations of theradiation characteristics due to varying ground properties cannot betolerated. 1n the past, elevated dipole antennas and the like were usedin such applications, but in order to overcome ground effects, suchantennas must be mounted a considerable distance above ground withrespect to the wavelength at the operating frequency. This results inthe necessity of constructing a supporting tower or framework. Theobvious disadvantages of such elevated antenna structures are that'theycreate a definite hazard to aircraft when used near aircraft runways asbeacon antennas, and they have high wind drag.

According to this invention a new, portable, low-profile antenna systemhas been developed which minimizes ground effects and eliminates theextra supporting tower,

or framework previously necessary to elevate the antenna in order toovercome ground effects.

In a preferred embodiment of this invention a metallic sheet, such asaluminum foil or a wire mesh, is imbedded in or coated with a rubberlikeplastic such 'as Mylar and is laid directly on the ground. Cavity-backedslot antenna elements are placed on the plastic covered sheet in anydesired arrangement, depending on the particular application, frequencyof operation, desired pattern, desired polarization, etc. The sheetextends beyond the antenna elements and minimizes ground effects.

Accordingly, it is an object of this invention to provide an antennasystem which is relatively immune to ground effects.

Another object of this invention is to provide a portable, low-profileantenna system.

A more specific object of this invention is to provide an antenna systemwhich minimizes ground effects without the use of elevated structures.

A further object of this invention is to provide a lowprofile antennasystem which has low wind drag.

Other objects and features of this invention will become apparent tothose skilled in the art upon consideration of the following detaileddescription taken in conjunction with the drawing, the single figure ofwhich shows a preferred embodiment of the invention.

Referring now to the drawing in detail, there is shown in a partiallycut away view a ground sheet 10 comprising a thin metallic layer '11covered on each surface by layers of suitable dielectric material 12.Sheet 10 is placed or laid directly on the ground or over water, and anumber of antenna elements 13 are mounted directly on the upper surfaceof sheet 10 in any desired arrangement depending upon the radiationpattern desired for particular applications. For purposes ofillustration, antenna elements 13 have been arranged to form a broadsidearray having Patented Feb. 11, 1964 three parallel rows of elements fedby .a coaxial input line lfi yvhich, in turn, is connected to a suitabletransmitter and/or receiver, not shown. With the feed system shown, theinputs to an antenna elements 13 are spaced V2) apart, where A is thewavelength at the operating frequency. This particular arrangement is anarrow-band, frequencysensitive antenna, and it was chosen for thisillustration because of its simplicity. For broad-band applications, afeed system having equal lengths of feed line to all elements 13 wouldbe used.

Each antenna element 13 is constructed having a sheet of dielectricmaterial 15, such as a flexible ferrite or styrofoam, covered on all itssurfaces but one with a metal conductive member 14. The open oruncovered surface of dielectric sheet 15 forms a slot in member 14.Energy is then fed to the mid-point of this slot from line 16. Eachantenna element 13 functions in the manner of a slot antenna backed by acavity which, in this case, consists of a stripline. The particularantenna elements shown were chosen because they have a low profile, forexample, at me. they extend only Auk or less above sheet 10, where )t isthe operating wavelength of the syswithout the necessity of thendetermining and compensating for or eliminating the ground effects foreach different installation.

A high degree of portability is obtained, especially when it isconsidered that sheet 10 is very thin and flexible and can be rolled uplike a blanket during transportation. For portable systems, the locationof the desired arrangementor arrangements of the antenna elements 13 canbe marked out on the upper layer 12 of sheet 10, facilitating properlocation of elements 13 when the system is set up in a new location.Antenna elements '13 may be fastened to sheet 10 by any suitable meansor they may be placed on sheet 10 without any fastening means whatsoeverdepending on the situation in which the antenna system is to be used.Direct connection of elements 13 to metal layer 11 is not necessarysince the capacity between the lower surface of elements 13 and layer 11is large, amounting to a short.

It is to be understood that the invention is not limited to theparticular type of antenna elements shown but that any cavity-backedslot antenna elements could be used. Also, the layer of metal foil 11 insheet 10 could be replaced by a layer of wire mesh if so desired. Wiremesh may be more desirable for high frequency installations covering alarge area; and in such installations, the mesh could be placed on topof wooden planks laid on the ground in place of using Mylar which wouldbe more expensive. The specific embodiment shown is merely illustrativeof the principles of the invention, and various changes andmodifications may be made without departing from the spirit and scope ofthe invention as set forth in the appended claims.

What is claimed is:

1. An antenna comprising a fiat, flexible sheet having an inner layerand two outer layers, said inner layer being of highly conductivematerial and said outer layers being of solid dielectric material, atleast one cavity-backed slot antenna element mounted directly on saiddielectric material and spaced from said highly conductive material, anda transmission line connected to said antenna element.

2. An antenna according to claim 1 where said inner layer is acontinuous sheet of metal foil.

3. An antenna according to claim 1 where said inner layer is a wiremesh.

4. An antenna comprising a substantially fiat, flexible ground sheethaving an inner layer of highly conductive material covered on eachsurface by a layer of solid di electric material, a plurality of spacedantenna elements mounted directly on the surface of said sheet in anarray, said antenna elements being unattached to said ground sheet andspaced from said highly conductive material, said ground sheet extendingbeyond the area covered by said antenna elements at least AA or more,where A is the wavelength at the operating frequency of said antenna,whereby said ground sheet acts to minimize ground effects, and atransmission line connected to said antenna elements.

5. An antenna according to claim 4 where said inner layer is acontinuous sheet of metal foil.

6. An antenna including a flat flexible shcct having at least twolayers, one of said layers being a highly conductive material and theother said layers being a dielectric material, at least onecavity-backed slot antenna element resting on said sheetand unattachedthereto, and a transmission line connected to said antenna element.

7. An antenna comprising in combination; a layer 0t highly conductivematerial covered on each surface by a layer of solid dielectricmaterial, and a plurality of cavitybacked slot-antenna elements mountedon said dielectric material and spaced from said conductive material,said slot-antenna elements being unattached to said conductive layer.

References Cited in the file of this patent UNITED STATES PATENTS1,685,875 Fishwick Oct. 2, 1928 2,364,084 Martin Dec. 5, 1944 2,433,369Kandoian Dec. 30, 1947 2,557,951 De Rosa et a1 June 26, 1951 2,684,444Fales July 20, 1954 2,840,819 McClellan June 24, 1958 2,929,065Kreinheder Mar. 15, 1960 2,993,205 Cooper July 18, 1961 2,996,713 BoyerAug. 15, 1961 3,096,520 Ehrenspeck July 2, 1963

1. AN ANTENNA COMPRISING A FLAT, FLEXIBLE SHEET HAVING AN INNER LAYERAND TWO OUTER LAYERS, SAID INNER LAYER BEING OF HIGHLY CONDUCTIVEMATERIAL AND SAID OUTER LAYERS BEING OF SOLID DIELECTRIC MATERIAL, ATLEAST ONE CAVITY-BACKED SLOT ANTENNA ELEMENT MOUNTED DIRECTLY ON SAIDDIELECTRIC MATERIAL AND SPACED FROM SAID HIGHLY CONDUCTIVE MATERIAL, ANDA TRANSMISSION LINE CONNECTED TO SAID ANTENNA ELEMENT.